Study of iodide as selective quencher of triplet excited states of pterin and lumazine introduction

M. PAULA DENOFRIO; CAROLINA LORENTE; PETER R. OGILBY; ANDRÉS H. THOMAS

C¨®rdoba

Congreso; XI Encuentro Latinoamericano de Fotoquímica y Fotobiología; 2012

It has been demonstrated that pteridines are able to act as efficient sensitizers in photoinduced oxidations. These processes have been well characterized using 2-aminopteridine-4(3H)-one (pterin; denoted Ptr) and pteridine-2,4(1,3H)-dione (lumazine; denoted Lum) as photosensitizers and the nucleotides 2¡ä-deoxyguanosine 5¡ä-monophosphate (dGMP) and 2¡ä-deoxyadenosine 5¡ä-monophosphate (dAMP) as oxidizable targets.(1-5)It is interesting to establish the nature, singlet (1S*) or triplet (3T*), of the sensitizer excited states involved in such processes. In this regard, the development and optimization of routine techniques that allow distinguishing from which excited state the photosensitization occurs becomes relevant. A good example is the use of certain species which, under controlled working conditions, can deactivate selectively an excited electronic state.(6)In this work, we present results of the selective deactivation of triplet excited states of Ptr and Lum by iodide anion. The method was applied to the reactions of dGMP and dAMP photosensitization previously studied. At low iodide concentrations, triplet states are deactivated, whereas singlet states do not. Under this conditions the photosensitized oxidation of nucleotides in the presence of pteridines is totally inhibited, demonstrating that the photooxidation process is initiated by pteridine triplet excited states. (1) Petroselli, G.; Erra-Balsells, R.; Cabrerizo, F. M.; Lorente, C.; Capparelli, A. L.; Braun, A. M.; Oliveros, E.; Thomas, A. H. Org. Biomol. Chem. (2007), 5, 2792-2799.(2) G. Petroselli, M. L. Dantola, F. M. Cabrerizo, A. L. Capparelli, C. Lorente, E. Oliveros, A. H. Thomas, J. Am. Chem. Soc. (2008), 130, 3001-3011.(3) M. P. Denofrio, S. Hatz, C. Lorente, F. M. Cabrerizo, P. R. Ogilby, A. H. Thomas, Photochem. Photobiol. Sci. (2009), 8, 1539¨C1549.(4) M. P. Denofrio, A. H. Thomas, C. Lorente, J. Phys. Chem. A (2010), 114,10944¨C10950.(5) M. P. Denofrio, M. L. D¨¢ntola, P. Vicendo, E. Oliveros, A. H. Thomas, C Lorente. Photochem. Photobiol. Sci., (2012), 11, 409-XXX(6) M. S. Kritsky, T. A. Lyudnikova, E. A. Mironov and I. V. Moskaleva, J. Photochem. Photobiol., B, (1997), 39, 43¨C48.